A fourth generation (4G) communication system, which is a next-generation communication system, is under development to provide users with services of various Quality of Service (QoS) levels at a data rate of about 100 Mbps. Particularly, the 4 G communication systems are advancing in order to support high speed services by guaranteeing mobility and QoS in Broadband Wireless Access (BWA) communication systems such as local area network systems and wireless metropolitan area network systems. Representative examples include an Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system.
According to the IEEE 802.16 system standard, a terminal transmits an uplink sounding signal to estimate a channel of a base station. Mostly, the sounding signal is defined as a set of orthogonal sequences, and the terminal transmits the sounding signal generated from one of the sequences. A plurality of terminals can transmit their sounding signals over the same resource. Hence, it is quite important to prevent interference between the sounding signals by maintaining the orthogonality between the sounding sequences. In a multi-cell environment, the same resource in the cells can be used as the sounding channel. In this case, the same sounding signals can be transmitted over the same resources in the neighboring cells, which cause Inter Cell Interference (ICI) of the sounding signal. That is, in the multi-cell environment, the ICI may greatly degrade the sounding performance.
Similar to the sounding signal, the ICI affects the system performance in relation to a reference signal transmitted in the downlink. The reference signal can be called a pilot signal. To compensate distortion of a data signal, the terminal needs to estimate the channel condition. The reference signal is used to estimate the channel condition. When the ICI occurs in the reference signal, the terminal can not accurately estimate the channel condition with a serving base station and not accurately estimate the distortion of the data signal. Consequently, the data transfer rate deteriorates. The reference signal is constituted in the form of the sequence similar to the sounding signal.
Thus, a solution is demanded to maintain the orthogonality between the sequences and to prevent the ICI for the sounding signal or the reference signal by obtaining the sequences as many as possible within the limited length.